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  • How much overhead is there in persistent connections?

    - by nynex
    Ok so I'm musing over a little side project I want to start. Essentially its a multi-session web based FTP client. Multi-session in that you can log into several FTP servers at the same time and perform operations like moving a file from one FTP server to another. I'm doing this mainly to brush up on the new webdev technologies, particularly websockets. I'm using node.js + socket.io to keep a persistent bi-directional connection between the web browser and the web server. The web server will also have persistent connections to each FTP server the user has logged into. So if there are 100 concurrent users each logged into 5 ftp accounts, the web server will have 100 websocket connections + 500 ftp connections. Is servicing 600 connections a lot? I know it depends on the hardware resources of the server but is something like this doable on a budget? Are there more efficient means of doing something like this? I know its unlikely that this project will really get popular but I want it to scale well regardless. Thanks for any help, I've still got a lot to learn.

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  • Can't figure out how to make Slitaz USB persistent

    - by Dennis Hodapp
    I installed Slitaz on my USB. However I can't figure out how to make it persistent automatically. There are different sources telling me different ways to make it persistent. One told me to add "slitaz home=usb" to the syslinux.cfg file like this: append initrd=/boot/rootfs.gz rw root=/dev/null vga=normal autologin slitaz home=usb but it didn't work for me. http://www.slitaz.org/en/doc/handbook/liveusb.html gave an example of how to do it manually but I didn't try it and I also want it to happen automatically. custompc.co.uk/features/602451/make-any-pc-your-own-with-linux-on-a-usb-key.html is an older article that also explains how to make the USB persistent but I don't want to try it cause it looks outdated (from 2008) does anyone know the best way to make the USB automatically persistent?

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  • php-fpm + persistent sockets = 502 bad gateway

    - by leeoniya
    Put on your reading glasses - this will be a long-ish one. First, what I'm doing. I'm building a web-app interface for some particularly slow tcp devices. Opening a socket to them takes 200ms and an fwrite/fread cycle takes another 300ms. To reduce the need for both of these actions on each request, I'm opening a persistent tcp socket which reduces the response time by the aforementioned 200ms. I was hoping PHP-FPM would share the persistent connections between requests from different clients (and indeed it does!), but there are some issues which I havent been able to resolve after 2 days of interneting, reading logs and modifying settings. I have somewhat narrowed it down though. Setup: Ubuntu 13.04 x64 Server (fully updated) on Linode PHP 5.5.0-6~raring+1 (fpm-fcgi) nginx/1.5.2 Relevent config: nginx worker_processes 4; php-fpm/pool.d pm = dynamic pm.max_children = 2 pm.start_servers = 2 pm.min_spare_servers = 2 Let's go from coarse to fine detail of what happens. After a fresh start I have 4x nginx processes and 2x php5-fpm processes waiting to handle requests. Then I send requests every couple seconds to the script. The first take a while to open the socket connection and returns with the data in about 500ms, the second returns data in 300ms (yay it's re-using the socket), the third also succeeds in about 300ms, the fourth request = 502 Bad Gateway, same with the 5th. Sixth request once again returns data, except now it took 500ms again. The process repeats for several cycles after which every 4 requests result in 2x 502 Bad Gateways and 2x 500ms Data responses. If I double all the fpm pool values and have 4x php-fpm processes running, the cycles settles in with 4x successful 500ms responses followed by 4x Bad Gateway errors. If I don't use persistent sockets, this issue goes away but then every request is 500ms. What I suspect is happening is the persistent socket keeps each php-fpm process from idling and ties it up, so the next one gets chosen until none are left and as they error out, maybe they are restarted and become available on the next round-robin loop ut the socket dies with the process. I haven't yet checked the 'slowlog', but the nginx error log shows lots of this: *188 recv() failed (104: Connection reset by peer) while reading response header from upstream, client:... All the suggestions on the internet regarding fixing nginx/php-fpm/502 bad gateway relate to high load or fcgi_pass misconfiguration. This is not the case here. Increasing buffers/sizes, changing timeouts, switching from unix socket to tcp socket for fcgi_pass, upping connection limits on the system....none of this stuff applies here. I've had some other success with setting pm = ondemand rather than dynamic, but as soon as the initial fpm-process gets killed off after idling, the persistent socket is gone for all subsequent php-fpm spawns. For the php script, I'm using stream_socket_client() with a STREAM_CLIENT_PERSISTENT flag. A while/stream_select() loop to detect socket data and fread($sock, 4096) to grab the data. I don't call fclose() obviously. If anyone has some additional questions or advice on how to get a persistent socket without tying up the php-fpm processes beyond the request completion, or maybe some other things to try, I'd appreciate it. some useful links: Nginx + php-fpm - recv() error Nginx + php-fpm "504 Gateway Time-out" error with almost zero load (on a test-server) Nginx + PHP-FPM "error 104 Connection reset by peer" causes occasional duplicate posts http://www.linuxquestions.org/questions/programming-9/php-pfsockopen-552084/ http://stackoverflow.com/questions/14268018/concurrent-use-of-a-persistent-php-socket http://devzone.zend.com/303/extension-writing-part-i-introduction-to-php-and-zend/#Heading3 http://stackoverflow.com/questions/242316/how-to-keep-a-php-stream-socket-alive http://php.net/manual/en/install.fpm.configuration.php https://www.google.com/search?q=recv%28%29+failed+%28104:+Connection+reset+by+peer%29+while+reading+response+header+from+upstream+%22502%22&ei=mC1XUrm7F4WQyAHbv4H4AQ&start=10&sa=N&biw=1920&bih=953&dpr=1

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  • Ubuntu: disable udev's persistent-net-generator.rules

    - by Luke404
    I'm using Ubuntu 12.04 LTS server edition and I am modifying /etc/udev/rules.d/70-persistent-net.rules to define my own mappings of ethernet interfaces to MAC addresses; that file is initially generated by rules in /lib/udev/rules.d/75-persistent-net-generator.rules at system installation time (or at the first boot, I actually don't know and it doesn't matter here). How can I be sure that my edited version will never ever be overwritten by anything? Removing the persistent-net-generator, as suggested on some websites, is not the Right Thing™ to do as told by comments in the file itself: it will be overwritten by any update of the udev package. I'm looking for a more formally correct way to disable it. Is it enough to just make sure that /etc/udev/rules.d/70-persistent-net.rules does exist? Maybe there are other events that could trigger its regeneration? (eg. adding or removing ethernet interfaces to the system?)

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  • Persistent Storage in Windows Phone 7

    - by Richard Jones
    Mark Arteaga – fellow MVP just helped me with this,  thought I’d share. Windows Phone 7 SilverLight supports persistent storage, which is a great way of saving settings betweens runs of your application. However I couldn’t get it to work. If you do this to create a persistant storage instance -    private IsolatedStorageSettings userSettings = IsolatedStorageSettings.ApplicationSettings; To retrieve settings do the following - string xx = userSettings[“SomeValue”].ToString();   Hiowever the bit that got me was how to save settings, you have todo this - userSettings.Add("Hello", DateTime.Now.ToShortTimeString());           userSettings.Save(); // <- This is the bit that got me   Hope this helps others

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  • Naming interfaces for persistent values

    - by orip
    I have 2 distinct types of persistent values that I'm having trouble naming well. They're defined with the following Java-esque structure, borrowing Guava's Optional for the example and using generic names to avoid anchoring: interface Foo<T> { T get(); void set(T value); } interface Bar<T> { Optional<T> get(); void set(T value); } With Foo, if the value hasn't been set explicitly then there's some default value available or pre-set. With Bar, if the value hasn't been set explicitly then there's a distinct "no value" state. I'm trying to optimize the names for their call sites. For example, someone using Foo may not care whether there's a default value involved, only that they're guaranteed to always have a value. How would you go about naming these interfaces?

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  • Moving from a traditional in memory Java session to persistent storage sessions

    - by Benju
    We have decided to take the plunge and move from using a typical java session provider in Tomcat/Jetty/etc to persisting everything to a central datastore. We are looking at using MongoDB for this. A few options come to mind... http://wiki.eclipse.org/Jetty/Tutorial/MongoDB_Session_Clustering This is nice because it will "auto-magically" persist our session to a Mongo installation. I am concerned however that we will not have fine grained control of what is happening. https://github.com/mattinsler/com.lowereast.guiceymongo/ GuiceMongo is interesting as it integrates with Guice. Perhaps we could persist everything via this ORM. Has anybody had to deal with this kind of move? It seems that moving from in memory to persistent session storage has a lot of gotchas.

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  • Explaining persistent data structures in simple terms

    - by Jason Baker
    I'm working on a library for Python that implements some persistent data structures (mainly as a learning exercise). However, I'm beginning to learn that explaining persistent data structures to people unfamiliar with them can be difficult. Can someone help me think of an easy (or at least the least complicated) way to describe persistent data structures to them? I've had a couple of people tell me that the documentation that I have is somewhat confusing. (And before anyone asks, no I don't mean persistent data structures as in persisted to the file system. Google persistent data structures if you're unclear on this.)

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  • something like persistent X forwarding?

    - by Arthur Ulfeldt
    I'm having trouble with the title on this one, please edit. When users connect to a VM with VNC/NX/RDP/other-tla they get a persistent desktop in a window . When they connect using ssh -X forwarding they get a local window managed by the local windo-manager that is not persistent. 1: is there a way to run a program on the VM and have it managed locally AND have it persistent? 2: can the client be on windows or OS-X? ps: in this case the vm's are running Ubuntu

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  • Persistent Spot Instance Request with CloudFormation

    - by PapelPincel
    Is it possible to create "Persistent Spot Instance" with AWS CloudFormation ? I'm going through the Autoscale and EC2 CloudFormation's template references but there is no mention how to set a property so the Spot requests stay persistent. When the price bid lower than the actual spot price AWS brings the instances down. I would like the instances to be started automatically when the instance price is cheaper again. This can be set manually when creating a new spot instance request by checking the option "Persistent Request" in the "Request Instances Wizard".

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  • Removing and adding persistent stores to a core data application

    - by mkko
    I'm using core data on an iPhone application. I have multiple persisntent stores that I'm switching from one to another so that only one of the stores can be active at the time. I have one managed object context and the different persistent stores are similar in data format (sqlite) and share the same managed object model. I'm importing the data to each persistent store from a respective XML file. For the first import everything works fine, but after I remove the imported data (the persistent store and the physical file) and then re-import, core data gives me an error: *** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'The NSManagedObject with ID:0x3c14e00 <x-coredata://6D14F11E-2EA7-4141-9BE8-53747DE6FCC6/Book/p2> has been invalidated.' This error comes from the save: of NSManagedObjectContext. Before re-importing, i'm removing the persistent store from the persistent store coordinator and removing the physical file, so everything should be as if re-importing was done for the first time. Alos, the objects in managed object context are removed and the context is sent the reset: message (I don't know if this is actually needed). Could some one help me out here? How should the persistent store be switched? I'm basically using the same logic as tutored here: http://blog.sallarp.com/iphone-core-data-uitableview-drill-down/ Thanks in advance.

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  • Create a Persistent Bootable Ubuntu USB Flash Drive

    - by Trevor Bekolay
    Don’t feel like reinstalling an antivirus program every time you boot up your Ubuntu flash drive? We’ll show you how to create a bootable Ubuntu flash drive that will remember your settings, installed programs, and more! Previously, we showed you how to create a bootable Ubuntu flash drive that would reset to its initial state every time you booted it up. This is great if you’re worried about messing something up, and want to start fresh every time you start tinkering with Ubuntu. However, if you’re using the Ubuntu flash drive to diagnose and solve problems with your PC, you might find that a lot of problems require guess-and-test cycles. It would be great if the settings you change in Ubuntu and the programs you install stay installed the next time you boot it up. Fortunately, Universal USB Installer, a great little program from Pen Drive Linux, can do just that! Note: You will need a USB drive at least 2 GB large. Make sure you back up any files on the flash drive because this process will format the drive, removing any files currently on it. Once Ubuntu has been installed on the flash drive, you can move those files back if there is enough space. Put Ubuntu on your flash drive Universal-USB-Installer.exe does not need to be installed, so just double click on it to run it wherever you downloaded it. Click Yes if you get a UAC prompt, and you will be greeted with this window. Click I Agree. In the drop-down box on the next screen, select Ubuntu 9.10 Desktop i386. Don’t worry if you normally use 64-bit operating systems – the 32-bit version of Ubuntu 9.10 will still work fine. Some useful tools do not have 64-bit versions, so unless you’re planning on switching to Ubuntu permanently, the 32-bit version will work best. If you don’t have a copy of the Ubuntu 9.10 CD downloaded, then click on the checkbox to Download the ISO. You’ll be prompted to launch a web browser; click Yes. The download should start immediately. When it’s finished, return the the Universal USB Installer and click on Browse to navigate to the ISO file you just downloaded. Click OK and the text field will be populated with the path to the ISO file. Select the drive letter that corresponds to the flash drive that you would like to use from the dropdown box. If you’ve backed up the files on this drive, we recommend checking the box to format the drive. Finally, you have to choose how much space you would like to set aside for the settings and programs that will be stored on the flash drive. Considering that Ubuntu itself only takes up around 700 MB, 1 GB should be plenty, but we’re choosing 2 GB in this example because we have lots of space on this USB drive. Click on the Create button and then make yourself a sandwich – it will take some time to install no matter how fast your PC is. Eventually it will finish. Click Close. Now you have a flash drive that will boot into a fully capable Ubuntu installation, and any changes you make will persist the next time you boot it up! Boot into Ubuntu If you’re not sure how to set your computer to boot using the USB drive, then check out the How to Boot Into Ubuntu section of our previous article on creating bootable USB drives, or refer to your motherboard’s manual. Once your computer is set to boot using the USB drive, you’ll be greeted with splash screen with some options. Press Enter to boot into Ubuntu. The first time you do this, it may take some time to boot up. Fortunately, we’ve found that the process speeds up on subsequent boots. You’ll be greeted with the Ubuntu desktop. Now, if you change settings like the desktop resolution, or install a program, those changes will be permanently stored on the USB drive! We installed avast! Antivirus, and on the next boot, found that it was still in the Accessories menu where we left it. Conclusion We think that a bootable Ubuntu USB flash drive is a great tool to have around in case your PC has problems booting otherwise. By having the changes you make persist, you can customize your Ubuntu installation to be the ultimate computer repair toolkit! Download Universal USB Installer from Pen Drive Linux Similar Articles Productive Geek Tips Create a Bootable Ubuntu USB Flash Drive the Easy WayCreate a Bootable Ubuntu 9.10 USB Flash DriveReset Your Ubuntu Password Easily from the Live CDHow-To Geek on Lifehacker: Control Your Computer with Shortcuts & Speed Up Vista SetupHow To Setup a USB Flash Drive to Install Windows 7 TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Test Drive Windows 7 Online Download Wallpapers From National Geographic Site Spyware Blaster v4.3 Yes, it’s Patch Tuesday Generate Stunning Tag Clouds With Tagxedo Install, Remove and HIDE Fonts in Windows 7

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  • Accessing a persistent ssh tunnel

    - by woowaa
    How do I pass commands (shell) to a persistent SSH tunnel rather than open a connection for every instance? I have a Python scraper running on a client server which passes URL variables and shell commands to a remote host via a reverse tunnel (forwarded port), so that the URL's are then executed on the host (python fabric ssh localhost:12345 'browser open URL'). I could make the reverse tunnel persistent but how do I echo the url/command to the session? Update - ControlMaster (built into SSH) solves this one.

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  • Installing MATLAB Ubuntu 12.10, persistent "permission denied" problem

    - by Javier
    I'm trying to install MATLAB on Ubuntu 12.10, I had it in my last laptop with 12.04 and I didn't have much trouble to install it. I'm getting this problem: j@jgb:~/Programs/Instaladores/matlab$ ./install Preparing installation files ... Installing ... ./install: 1: eval: /tmp/mathworks_1436/sys/java/jre/glnxa64/jre/bin/java: Permission denied Finished And it doesn't change if I change the permissions to the java file or to the install file as other posts say. In my /etc/fstab file I had this line added (But nothing changes if I comment it): tmpfs /tmp tmpfs nodev,nosuid,noexec,mode=1777 0 0 Thanks

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  • Persistent "held broken packages" error

    - by stoplan
    sudo apt-get update && sudo apt-get install netflix-desktop gives the error The following packages have unmet dependencies: netflix-desktop : Depends: wine-browser-installer but it is not going to be installed E: Unable to correct problems, you have held broken packages. but dpkg --get-selections | grep hold shows nothing. I'm running 12.04 64-bit. I've followed the directions in How do I resolve unmet dependencies?: Confirmed that main, universe, restricted and multiverse software sources are enabled sudo apt-get clean sudo apt-get -f install (returning '0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.') sudo dpkg --configure -a sudo apt-get -f install (again '0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.) sudo apt-get -u dist-upgrade (0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.) used Y PPA Manager to check for duplicate ppas (none found) [Edit] I have had the same error with other packages. Here's the output requested by Alaa: sudo apt-get install wine-browser-installer Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: wine-browser-installer : Depends: wine-compholio (= 1.5.19~precise1) E: Unable to correct problems, you have held broken packages.

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  • Strategy for backwards compatibility of persistent storage

    - by Baqueta
    In my experience, trying to ensure that new versions of an application retain compatibility with data storage from previous versions can often be a painful process. What I currently do is to save a version number for each 'unit' of data (be it a file, database row/table, or whatever) and ensure that the version number gets updated each time the data changes in some way. I also create methods to convert from v1 to v2, v2 to v3, and so on. That way, if I'm at v7 and I encounter a v3 file, I can do v3-v4-v5-v6-v7. So far this approach seems to be working out well, but I haven't had to make use of it extensively yet so there may be unforseen problems. I'm also concerned that if the objects I'm loading change significantly, I'll either have to keep around old versions of the classes or face updating all my conversion methods to handle the new class definition. Is my approach sound? Are there other/better approaches I could be using? Are there any design patterns applicable to this problem?

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  • Non persistent keyboard shortcuts in Unity

    - by nblumoe
    I did change the keyboard shortcuts for window navigation in Unity to use hjkl (vim movement). I did reassign the shortcuts via GUI in System Settings Keyboard Shortcuts. Here are two examples of the assigned shortcuts: Move window one workspace to the left = Shift+Ctrl+Alt+H Switch to workspace left = Ctrl+Alt+H Occasionally, when restarting the maching, these shortcuts are being reset to theit default values: Move window one workspace to the left = Shift+Ctrl+Alt+Left Switch to workspace left = Ctrl+Alt+Left How can I make these changes permanent? Can someone help me, narrowing down the problem?

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  • In a pinch, is it worthwhile to run a bootable USB drive for my primary PC for an extended period?

    - by jason
    My hard drive has crashed, and I won't be able to buy a new one for a month or two. I've got a 16GB USB 3.0 flash drive that I'd like to have running a persistent ubuntu or ubuntu gnome distro. While it's not the best solution, is it a solution, or is it just a good way to wear out a flash drive? I plan on mostly storing things in Google Drive, so other than wearing out the flash drive, are there any risks involved?

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  • How to run a bootable USB drive as my primary PC for an extended period?

    - by jason
    My hard drive has crashed, and I won't be able to buy a new one for a month or two. I've got a 16GB USB 3.0 flash drive that I'd like to have running a persistent ubuntu or ubuntu gnome distro. While it's not the best solution, is it a solution, or is it just a good way to wear out a flash drive? I plan on mostly storing things in Google Drive, so other than wearing out the flash drive, are there any risks involved?

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  • Persistent connections with pipelining

    - by Summer_More_More_Tea
    Hi: I have a question about the behavior of a browser( especially Firefox ) tackling with persistent connections: Must all the requests sent in one pipelined persistent connection direct to the same server? What about a request specified by user from address bar -- may it reuse an already established persistent connection to send its request or need another connection? Regards.

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • HTTP Non-persistent connection and objects splitting

    - by Fabio Carello
    I hope this is the right board for my question about HTTP protocol with non-persistent connections. Suppose a single request for a html object that requires to be split in two different HTML response messages. My question is quite simple: do the connection will be closed after the first packet dispatch and then the other one will be sent on a new connection? I can't figure out if the non-persistent connection is applied at "single object level" (does't care if on multiples messages) or for every single message. Thanks for your answers!

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  • making cookies persistent in IE8

    - by Jamie Stevens
    There's a website I sign into frequently, and I'm getting sick of entering my username and password every time. The website can remember who I am so long as I don't close my browser (Internet Explorer 8), but when I do it forgets me, and asks me to login again. I'm guessing this is because it's using a cookie (and perhaps a session) that expires when I close my browser. Is there anyway to make this information persistent across each time I load my browser? (I tried exporting the cookies to a file, and then importing them as soon as the browser was reloaded, but that didn't work either... I'm thinking the cookie text file needs to be modified somehow.) (FYI The website is http://blackboard.unh.edu, but you won't have access unless you happen to be a student there :-) NOTE: I'm not interested in using any password remembering features in the browser. The only solution I'm open to is making the cookie / session persistent somehow!

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